Vapor generator

ABSTRACT

A vapor generator adapted for use in a ship propulsion system requiring both superheated and reheated steam for ahead operation and only superheated steam for astern operation, the vapor generator having two parallel gas flow passes with dampers to regulate gas flow therethrough and including serially connected sections of superheater surface disposed in both of the gas passes and an attemperator connected to receive vapor from a first set of the superheater sections for flow therethrough to a second set of the superheater sections, where each set of sections is disposed in both gas passes.

United States Patent Neil P. Billie LondomEnghnd Sept. 22, 1969 Aug. 31, 1971 Babcock 8: Wilson, Limited London, Enghnd Sept. 23, 1968 Great Britain Inventor Appl. No. Filed Patented Assignee Priority VAPOR GENERATOR 7 Claims, 5 Drawing Figs.

US. Cl. 122/478, 60/73, 122/480 Int. Cl F22g 7/14 Field 01 Search 60/73; 122/478, 480

[56] References Cited UNITED STATES PATENTS 2,879,752 3/1959 Hutchings 122/480 3,280,559 10/1966 Hutchings 60/73 3,364,904 1/1968 Hutchings 122/480 Primary Examinerl(enneth W. Sprague Attorney-J Maguire ABSTRACT: A vapor generator adapted for use in a ship propulsion system requiring both superheated and reheated steam for ahead operation and only superheated steam for astem operation, the vapor generator having two parallel gas flow passes with dampers to regulate gas flow therethrough and including serially connected sections of superheater surface disposed in both of the gas passes and an attemperator connected to receive vapor from a first set of the superheater sections for flow therethrough to a second set of the superheater sections, where each set of sections is disposed in both gas passes.

PATENIEU AUB31 l97| 3.602.201

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Neil P. Baillie m B Y ATTORNEY PATENTEU M1631 \sn 180? Pm sum 2m 5 VAPORGENERATOR This invention relates to ship propulsion-power plant and particularly to vapor. generating and superheating units in such plant.

In British PatentNo. 1,050,913 which issued on Dec. 14,

1966, we describe, for a ship propulsion unit, a vapor generating and superheating unit adapted .to supply superheated and reheated vapor for .ahead operation and superheated vapor for astern operation which includes a furnace chamber, a first gas pass arranged forthe flow therethrough of combustion gases generated in the furnace chamber and having a first portion of superheating means therein, a second gas pass arranged for the flow therethrough in parallel with the first gas pass of combustion gases generated in the furnace chamber and having therein reheating means and, upstream as regards gas flow of thereheating means, a. second portion of superheating means, dampermeans proportioning-the flow of combustion gases between the first and second gas passes and vapor attemperating means.

When .the ships propulsion plantis operated to drive the ship ahead, the said vapor generator is required to provide superheated -vapor for the prime mover, e.g. vapor turbine means, and to reheat the vaponbetween stages of the prime mover. The temperatureof the reheated vapor delivered to the prime mover may be regulated, e.g. automatically, by adjustment of the damper proportioning the gas flow between the two passes. The temperature of the superheated vapor deliverer to the prime mover may be regulated by adjusting the control means of the vapor attemperatingmeans, which may be.provided in thevapor conduit from the superheating,

means to the prime mover or in a vapor conduit conducting partly superheatedvapor from'the superheating means in the second pass to thesuperheating means in thefirst pass. As compared withan arrangementinwhichall the superheating means lie in the first pass, the said arrangement described in the Patent secures that if at a constant load the dampers are readjustedto correct any change that might occur for any reason in reheat temperature, thensince thechange inthe heat absorption in the second pass superheating means is in the opposite sense to the changein-the heat absorption in the first pass superheating means the totalheat absorption for superheating will be-unchanged or itwill tend to change less. Moreover, in view of the portion of superheating means in front of the reheating means, the arrangementmakes it possible to design for and operate with high gas temperatures at the entry to the second pass yet withsatisfactorily reduced gas temperatures at the reheating means. The protection of the reheating means from high gas temperatures is particularly important when the ships propulsionplant is operated to drive the ship astern, when the vapor generator unit is not required to reheat vapor between prime mover stages and no vapor therefore passes through reheating means, for which circumstances the dampers controlling the gas flow through the second pass are closed but in spite of the closure thereof combustion gases usually penetrate into the second pass and impinge upon the reheating means. Under such astem operation, moreover, since not all the superheating means lie in the first pass, the heat absorption in the. superheating means is lower than the considerably excessive magnitude it would have if all the superheating means lay in the first pass.

The percent invention comprises in a ship propulsion plant a vapor generating and superheating unit adapted to supply superheated and reheated vapor for ahead operation and superheated vapor for astern operation which includes a furnace chamber, a first gas pass arranged for the flow therethrough of combustion gases generated in the furnace chamber'and having a first portion of superheating means therein, a second gas pass arranged for the flow therethrough in parallel with the firstgas pass of combustion gases generated in the furnace chamber and having therein reheating means and upstream as regards gas flow of the reheating means, a second portion of superheating means, damper means proportioningthe flow of combustion gases between the first and second gas passes and vapor attemperating means, wherein each pass includes two superheater sections, the superheating means of the unit comprising two superheater'sections, one in each pass, arranged for serial flow therethrough of vaporbefore it is cooled in the vapor attemperating means and two superheatersections, one in each pass, arranged forserial'flow therethrough of vvapor after it has been cooled in the attemperating means.-

The arrangement whereby the attemperating means, by which superheat temperature may be regulated when in ahead operation the reheat temperature is regulated by damper adjustment, is positioned at an intermediate stage in the vapor flow in relation to the superheating means of the unit makes it possible to operate without excess superheat temperatures at the final outlet from the superheating means. The arrangement further develops the previously mentioned proposal to place in the two passes respective portions of the superheating means, by placing in the two passes respective sections of the part of the superheating means prior to the attemperating means, which part maybe termed the primay superheater, and by placing in the two passes respective sections of the part of the superheating means subsequent to the attemperating means, which part may be termed the secondary superheater. During ahead operation of the ships propulsion unit, if at a constant load the dampers are repositioned to correct a variation in reheat temperature, the opposition or compensation between the increase inonepass and the decrease in the other pass of heat absorption for superheating purposes is accompanied by the opposition or compensation between the increase in heat absorptionin one primary superheater section and the decrease in heat absorption in the other primary superheater section, that is to say, it is accompanied by less change in the temperature of the vapor arriving at the attemperating means than if alltheprimary superheater were in one pass and all the secondary superheater in the other pass.

Most suitably, the attemperating means are of the-indirect contact type. Attemperatingmeans of indirect contact type for this purpose are preferably of the kind comprising, in parallel with a bypass connection, tubes in loops or coils cooled externally by liquid of the vapor generator at evaporation temperature, for example, tube loops immersed in a lower or mud drum of the vapor generator. However, we do not exclude the possibility that for the attemperating means of the indirect contact type the cooling medium might be combustion air or feedwater for the vapor generator. The hotter or less hot the vapor entering such attemperating means the larger or smaller respectively are the temperature differences therein by which heat is withdrawn from the vapor and thus even if the control means for the attemperating means had a fixed setting the temperature variations in vapor leaving the attemperating means would be smaller than the temperature variations in vapor arriving at the attemperating means.

It is considered that the smallness of the change in the control setting of the attemperating means that may be required to compensate for the departure from constancy of the final superheat temperature if,- at a constant load, the dampers are repositioned to correct a reheat variation, will, more particularly when the attemperating means is of the indirect contact type, reduce the possibility of clashes under some circumstances between the operations of the automatic control system for reheat regulation and the automatic control system for superheat regulation.

If the departure from constancy of the final superheat temperature when, at normal steaming load, the dampers are adjusted for reheat regulation is zero or sufficiently small it might be possible to operate with a fixed setting of the attemperator controls during normal steaming, which may account for at least percent of the operating time of the ship's propulsion unit. lt is possible that for the remaining small proportion of the operating time, when the ship is being maneuvered, it might be found that another fixed setting of the said controls obliging a greater proportion of the vapor flow to pass through cooled coils and a smaller proportion through the bypass thereto, gave tolerable conditions. In this case the at temperator controls would normally be in either one or the other of two fixed settings and it might not be greatly advantageous to provide automatic controls for superheat regulation.

It will be understood that if the load is varied, control of the attemperating means will be essential if, in addition to regulating reheat by damper control, it is required to regulate superheat. Attemperating means of the indirect contact type will tend to absorb more heat from the steam flow at higher loads than at lower leads and thus even if uncontrolled have a tendency of themselves to flatten the superheat characteristic.

During astem operation, when no vapor flows through the reheating means and the dampers controlling the second pass are closed, the reheating means are protected by the primary and secondary superheater sections in the second pass upstream of the reheating means. Since the primary superheater includes a section in the first pass the attemperating means receives substantially superheated vapor and is therefore able to exercise substantial control over the superheat temperature.

The invention has been devised in connection with the design of and more particularly for application to reheat marine boilers of the radiant type which with a view to compactness and efiiciency have a relatively small furnace chamber which the combustion gases leave at high temperature.

The invention will now be described by way of example with reference to the accompanying partly diagrammatic drawings, in which FIG. 1 is a side elevation of a marine reheat boiler in section on the line ll of FIGS. 3 and 4,

FIG. 2 is a side elevation of the boiler in section on the line 11- of FIGS. 3 and 4,

FIG. 3 is a front elevation of the boiler in section on the line lll-lll of FIGS. 1 and 2,

FIG. 4 is a plan of the boiler in section on the line lV-lV of FIGS. 1,2and3and FIG. 5 is a diagram showing the scheme of steam flow through the superheater sections of the boiler.

' Referring to FIGS. 1 to 4 of the drawings, the boiler setting of a marine reheat boiler of the radiant type, in which the superheating means comprise four superheater sections, as will be described, is divided by a transverse tube wall 11 to form a furnace chamber 12 and an upflow passage 13 at the rear thereof. The tubes 14in the said tube wall extend upwardly from a header 15 initially in staggered relationship to define a screen 16 of spaced tube limbs at the entry of the upflow passage 13 and then as a single row continue first vertically and then, when adjacent the boiler separator drum 17, steeply upwardly and rearwardly to terminate in the said drum. A second set of tubes 18 extends from the header l5 forwardly at an upward inclination to define the floor 19 of the furnace chamber, then vertically to define the front wall 20 of the setting and then rearwardly at a slight upward inclination to define the roof 21 of the furnace chamber, which roof is formed with a row of four burner ports'22 with oil burners 23, after which the second set of tubes 18 extends upwardly to terminate in the drum 17. Above the roof is a wind box 24 for the vburners. A third set of tubes 25 extends from the header 15 rearwardly at an upward inclination to define the floor 26 of the upflow passage 13, then, defining the rear wall 27 of the setting, first vertically and then steeply upwardly and rearwardly, and finally forwardly at an upward inclination, in staggered formation to allow gas flow therepast, across the upflow passage 13 to terminate in the drum 17. Each sidewall 31 of the furnace chamber is defined by a set of tubes 32 extending from a lower header 33 to an upper header 34 which is connected to an upriser (not shown) to the drum 17 and each sidewall 35 of the upflow passageis defined by a set of tubes 36 extending from a lower header 37 to an upper header 38 which is connected by an upriser (not, shown) to the drum l7.

The upflow passage is divided by a division wall 39 extending parallel to the sidewalls 35 of the passage and formed by a set of tubes 40 extending between a lower header 41 and an upper header 42 which is connected by an upriser (not shown) to the drum l7. Downcomers (not shown) extend from the drum [7 to supply water to the four lower headers 33 and 37, feeders (not shown) extend from the four lower headers 33 and 37 to supply water to the lower header 15 and a feeder (not shown) extends from one of the two lower headers 37 to supply water to the lower header 41.

Of the two gas passes into which the upflow passage 13 is divided by the wall 39 one pass 43 is of about four-sevenths the width of the other pass 44 and contains in its upper part two tube banks 45, one above the other, of economizer tubes, which extend in parallel flow with the gas flow from a lower inlet header 51 to an upper outlet header 52. Below the economizer bands 45 in the first pass 43 is a tube bank 53 forming a secondary superheater section, comprising tubes extending in counterfiow to the gas flow from an upper inlet header 54 to a lower outlet header 55, and below the secondary superheater section 53 in the first pass is a tube bank 56 forming a primary superheater section, comprising tubes extending in parallel flow with the gas flow from a lower inlet header 57 to an upper outlet header 58. In the upper part of the second, wider gas pass 44 are two tube banks 59, one above the other, comprising the reheater of the boiler formed by tubes extending in counterfiow to the gas flow from an upper inlet header 60 to a lower outlet header 61. Below the reheater in the second pass is a tube bank 62 forming another secondary superheater section, comprising tubes extending in counterflow to the gas flow from an upper inlet header 63 to a lower outlet header 64 and below the secondary superheater 62 in the second pass is a tube bank 71 forming another primary superheater section, comprising tubes extending in parallel flow with the gas flow from a lower inlet header 72 to an upper outlet header 73. Each of the tubes of the various above-mentioned banks in the gas passes extends with horizontal limbs sinuously forwards and backwards in the pass in which it is arranged. The tube bank inlet and outlet headers are outside the upflow passage 13 to the rear of the rear wall 27.

Immediately above the level of the sidewall and division wall upper headers 34 and 42 is a row of dampers 74 for controlling the flow of gases in the first pass 43 and a row of dampers 75 for controlling the flow of gases in the second pass 44 to an upper undivided part 76 of the upflow passage 13, which before leading to a stack (not shown) accommodates a further economizer bank 77.

Within a longitudinally extended region of the separator drum 17 there are provided attemperating means of the indirect contact type, denoted by 78, comprising two longitu dinally extending tube bundles in the drum water space, sideby-side, the tubes of each bundle connecting into inlet and outer headers (not shown) of cylindrical form and the tube bundles being connected for parallel flow of steam therethrough. Within another longitudinally extended drum region there are provided desuperheating means of the indirect contact type, denoted by 79, comprising two longitudinally extending tube bundles in the drum water space, similar to the attemperator tube bundles but connected for serial flow of steam therethrough.

Steam conduits (not shown in FIGS. 1 to 4) are provided which, in accordance with the steam flow scheme indicated in FIG. 5, connect the various primary and secondary superheater sections in series in the steam flow path from the separator drum to the point of use. Referring to FIG. 5, the saturated steam from the steam space of the separator drum 17 is led to the inlet header 72 of the primary superheater section 71 in the second pass 44. The steam, after flowing generally upwardly in the said section, is led from the outlet header 73 thereof to the inlet header 53 of the primary superheater section 56 in the first pass 43 in which it also flows generally upwardly. The steam is led from the outlet header 58 of the said section to a three-way valve 80 the adjustment of which determines the proportion of the steam flow which shall pass through the attemperating means 78 while the remaining proportion of the steam flow passes through a bypass 81 to the attemperating means. The two proportions of the steam flow rejoin and pass to the inlet header 63 of the secondary superheater section 62 in the second pass 44. The steam, after flowing generally downwardly in the said section, is led from the outlet header 64 thereof to the inlet header 54 of the secondary superheater section 53 in the first pass 43 in which it flows generally downwardly. The steam finally is led from the outlet header 54 of the said section, for ahead operation of the ships propulsion unit, to a high pressure steam turbine (not shown) and, for reverse operation of the unit, to a reversing turbine (not shown). In ahead operation, steam is led from a reduced pressure stage of the main steam turbine system through the reheater 59 in which it flows generally downwardly, and thence back to a low pressure stage of the main steam turbine.

Steam required for auxiliary machines off the ship is taken from the steam conduit supplied by the final outlet header 54 and led to such machines after passing through the desuperheating means 79.

In the operation of the propulsion plant to drive the ship ahead, the boiler furnace chamber 12 is fired to generate steam at the desired rate and at the desired pressure for the high pressure steam turbine of the main steam turbine system, the dampers are adjusted so that the reheater 59, resuperheating steam from a reduced pressure stage of the main steam turbine system, heat it to the desired temperature for the low pressure turbine of the main steam turbine system and the three-way valve 80 is adjusted so that, as the result of the operation of the attemperating means 78, cooling a corresponding proportion of the steam from the primary superheater sections 71 and 56, steam passes to the secondary superheater sections 62 and 53 at a temperature which results in a steam temperature at the final superheated steam outlet header 55 which is that desired at the said high pressure steam turbine.

If at a constant load the dampers are readjusted to correct a variation in reheat temperature, then, since there is a primary superheater section in each gas pass, whereby there will generally be only a relatively small change in the temperature of the steam arriving at the attemperating means 78, and since also the attemperating means 78 tends to withdraw more heat from hotter steam than from cooler steam and since moreover there is a secondary superheater section in each gas pass, whereby there will generally be only a relatively small change in the steam temperature rise'from the inlet header 63 to the outlet header 55, there will generally be only a small change required in the adjustment of the three-way valve 80 to ensure that the steam temperature at the final superheated steam outlet header 55 remains constant.

If the load is varied, it will generally be necessary, as well as changing the firing rate and readjusting the dampers, also to readjust the three-way valve 80, since all the four superheater sections are convectively heated. However, since the attemperating means 78 absorb more heat from the steam at higher steam temperatures and flow rates than at lower steam temperatures and flow rates, the final superheated steam temperature is not difficult to regulate.

The disposition of the primary superheater section 56 upstream of the secondary superheater section 53 in the first gas pass 43 and the disposition of the primary superheater section 71 upstream of the secondary superheater section 62 in the second gas pass 44 are adapted for the protection of the superheater tubes first impinged on by the furnace chamber gases as astem, the furnace chamber 12 is fired to enerate steam at he desired rate and at the desired pressure or the reversing turbine, the dampers 75 are closed since the reversing turbine does not require resuperheated steam and the three-way valve 80 is adjusted so that the steam delivered to the reversing turbine has the desired temperature which may be the same as that required by the high pressure steam turbine used for ahead operation. The reheater 59 is protected by the superheater sections 71 and 62 in the second pass, the more so since the primary superheater section 71 receives saturated steam and the secondary superheater section 62 receives steam directly from the attemperating means and its bypass. in view of the primary superheater section 56 in the first pass 43 substantially superheated steam arrives at the three-way valve 80 and thus the attemperating means 78 are able to exercise sub stantial control over the temperature of the steam delivered to the reversing turbine.

What is claimed is:

1. in a ship propulsion plant a vapor generating and superheating unit adapted to supply superheated and reheated vapor for ahead operation and superheated vapor for astern operation which includes a furnace chamber, a first gas pass arranged for the flow therethrough of combustion gases generated in the furnace chamber and having a first portion of superheating means therein, a second gas pass arranged for the flow therethrough in parallel with the first gas pass of combustion gases generated in the furnace chamber and having therein reheating means and, upstream as regards gas flow of the reheating means, a second portion of superheating means, damper means proportioning the flow of combustion gases 7 between the first and second gas passes and vapor attemperating means, wherein each pass includes two superheater sections, the superheating means of the unit comprising two superheater sections, one in each pass, arranged for serial flow therethrough of vapor before it is cooled in the vapor attemperating means and two superheater sections, one in each pass, arranged for serial flow therethrough of vapor after it has been cooled in the attemperating means.

2. A vapor generator as claimed in claim 1, wherein the attemperating means are of the indirect contact type.

3. A vapor generator as claimed in claim 1, wherein of the said two superheater sections prior to the attemperating means that first traversed by the vapor lies in the second pass.

4. A vapor generator as claimed in claim 1, wherein of the said two superheater sections subsequent to the attemperating means that first traversed by the vapor lies in the second pass.

5. A vapor generator as claimed in claim 3, wherein each gas pass the superheater section prior to the attemperating means is upstream, as regards gas flow, of the superheater section subsequent to the attemperating means.

6. A vapor generator as claimed in claim 5, wherein in each gas pass the superheater section prior to the attemperating means is arranged for upflow of vapor therein.

7. A vapor generator as claimed in claim 5, wherein in each gas pass the superheater section subsequent to the attemperating means is arranged for vapor flow therein in counterflow with combustion gas flow thereover. 

1. In a ship propulsion plant a vapor generating and superheating unit adapted to supply superheated and reheated vapor for ahead operation and superheated vapor for astern operation which includes a furnace chamber, a first gas pass arranged for the flow therethrough of combustion gases generated in the furnace chamber and having a first portion of superheating means therein, a second gas pass arranged for the flow therethrough in parallel with the first gas pass of combustion gases generated in the furnace chamber and having therein reheating means and, upstream as regards gas flow of the reheating means, a second portion of superheating means, damper means proportioning the flow of combustion gases between the first and second gas passes and vapor attemperating means, wherein each pass includes two superheater sections, the superheating means of the unit comprising two superheater sections, one in each pass, arranged for serial flOw therethrough of vapor before it is cooled in the vapor attemperating means and two superheater sections, one in each pass, arranged for serial flow therethrough of vapor after it has been cooled in the attemperating means.
 2. A vapor generator as claimed in claim 1, wherein the attemperating means are of the indirect contact type.
 3. A vapor generator as claimed in claim 1, wherein of the said two superheater sections prior to the attemperating means that first traversed by the vapor lies in the second pass.
 4. A vapor generator as claimed in claim 1, wherein of the said two superheater sections subsequent to the attemperating means that first traversed by the vapor lies in the second pass.
 5. A vapor generator as claimed in claim 1, wherein each gas pass the superheater section prior to the attemperating means is upstream, as regards gas flow, of the superheater section subsequent to the attemperating means.
 6. A vapor generator as claimed in claim 5, wherein in each gas pass the superheater section prior to the attemperating means is arranged for upflow of vapor therein.
 7. A vapor generator as claimed in claim 5, wherein in each gas pass the superheater section subsequent to the attemperating means is arranged for vapor flow therein in counterflow with combustion gas flow thereover. 